Wavelength converted light emitting diodes (LEDs) are becoming increasingly important for illumination applications where there is a need for light of a color that is not normally generated by an LED, or where a single LED may be used in the production of light having a spectrum normally produced by a number of different LEDs together. One example of such an application is in the back-illumination of displays, such as liquid crystal display (LCD) computer monitors and televisions. In such applications there is a need for substantially white light to illuminate the LCD panel. One approach to generating white light with a single LED is to first generate blue light with the LED and then to convert some or all of the light to a different color. For example, where a blue-emitting LED is used as a source of white light, a portion of the blue light may be converted using a wavelength converter to yellow light. The resulting light, a combination of yellow and blue, appears white to the viewer.
In some approaches, the wavelength converter is a layer of semiconductor material that is placed in close proximity to the LED, so that a large fraction of the light generated within the LED passes into the converter. WO2009/048704 describes a light emitting diode (LED) that includes a wavelength converter for converting the wavelength of light emitted by the LED. A bonding layer attaches the LED wafer to the wavelength converter. Another approach is direct wafer bonding of the semiconductor wavelength converter to the semiconductor material of the LED die.